Abstract: In order to investigate the gas pressure relief permeability increase effect of hydraulic disturbance to soft coal and sandstone,and overcome the blindness of adopting high pressure water injection to increase the concentration and efficiency of coal seam gas.Hydraulic disturbance experiments on cubic sandstone and soft coal body samples are carried out with the self designed modified “true triaxial hydraulic disturbance gas seepage test device”.The law of crack development and extension about the two cubic samples during the water injection are obtained according to the analysis about the real time pumping pressure evolution curve of pumping pressure:undergoing fractured multiple fractured completely broken,finally completely fractured by high pressure water during the pumping process,and its internal fractures fully expanded and derived,and finally forming intercon nected fracture network.On the contrary,undergoing fractured compacted closed,the soft coal samples are finally compacted and closed,and the internal fracture network fails to expand and communicate.The applicability of hydraulic disturbance to the two kinds of samples is experimentally validated based on the permeability comparative analysis before and after hydraulic disturbance:the permeability of soft coal samples almost loses.In the test coal mine,the fracturing boreholes are arranged in the soft coal seam and its roof sandstone respectively for the verification corresponding to the simulation experiment,the gas drainage effect after hydraulic disturbance is investigated adopting the relative indicators:after hydraulic disturbance,the gas drainage flow rate,the concentration and purity of sandstone drilling increase greatly,and the attenuation coefficient decreases sharply,however,the corresponding indexes of soft coal seam drilling shows the opposite trend.Both experimental results and field practice show that the brittle deformation occurs within the sandstone under the action of hydraulic disturbance,the internal fracture develops,extends and penetrates well under the action of continuous high water pressure,the well developed network system forms,providing a smooth flow channel for the gas desorption,diffusion and migration from the lower coal body.On the contrary,in the initial stage of hydraulic disturbance,there are cracks in the soft coal body,but as the water injection continues,plastic deformation occurs inside the coal body,natural and man made cracks (gaps) are blocked by coal slime mixed with water and coal body,and the coal body is gradually compacted,gas fluidity weaken,and gas permeability decreases.The research results show that for soft coal body,transferring the hydraulic disturbance object to its hard roof is one of the effective ways to relieve pressure and increase permeability in soft coal seam,it is expected to achieve ideal gas control effect when it is applied to low permeability outburst coal seam which is unsuitable for hydraulic disturbance.